The light distribution emitted from a typical light emitting diode (LED) is Lambertian, which means the highest light intensity is directly above the emitting surface of the LED. In typical lighting applications such as street lights, multiple LEDs are mounted on a flat surface all facing downwardly toward the street. If the Lambertian LED light emission pattern is not modified by an additional optical component, most of the light intensity is directed directly below the street light luminaire onto the street, thus generating an unwanted hot spot under the luminaire and minimal light directed to the area around the street light. For most street light applications, there is a wide target area of illumination that extends beyond the hot spot that would be directly underneath the luminaire. Consequently, a wider and more uniform illumination distribution on the street or other desired illuminated areas can be difficult to achieve.
Secondary lenses mounted over the LEDs are often used to more uniformly redistribute the light emitted from the LEDs so that the adjacent target area around the LED luminaire is better illuminated (e.g. in order to meet various IESNA light distribution criteria for the street lighting or other area lighting applications). However, in certain applications, it may be desired to selectively exclude a portion of the adjacent area around the luminaire from the distribution of light. For example, in residential street light applications, many times street lights are positioned adjacent to houses, where a substantially uniform distribution of the light over a large target area causes too much light to be directed toward adjacent homes. Rather, it is desired that the street light illuminate the street and sidewalks of the target area, but reach not much further toward an adjacent home where it would interfere with the privacy of the residents. Asymmetric secondary lenses could be used to redirect some of the light away from an adjacent home, but such lenses are difficult and expensive to implement, and provide only limited success in preventing light from being directed into an adjacent area while still maintaining the desired uniform (or substantially uniform) distribution of light in the remaining portions of the target area.
There is a need for an LED luminaire that efficiently and reliably produces the desired illumination of light in an adjacent around the luminaire with the ability to selectively reduce or eliminate illumination of light in one portion of that adjacent area without adversely affecting the distribution of light elsewhere.